1. Field of the Invention
The present invention relates to a vehicle including a duct configured to take in air from outside by utilizing a ram pressure.
2. Description of the Related Art
An engine mounted in a vehicle such as a motorcycle includes a cylinder head having a combustion chamber. An air-intake passage is coupled to an intake port of the combustion chamber to guide air and fuel to the combustion chamber. Typically, the air-intake passage includes an air cleaner box of an air cleaner, an air-intake duct, and a throttle body of a throttle device which are coupled to each other in this order from upstream side in an air flow direction. Inside the throttle body, a throttle valve for controlling an air-intake amount and an injector for injecting a fuel are provided.
Japanese Laid-Open Patent Application Publication No. 2007-64061 discloses that in a ram-air air-intake passage configured to take in air from outside efficiently by utilizing the ram pressure, a duct is disposed to extend from an air inlet of an air cleaner box to a front end portion of a vehicle, and an air inlet at a tip end of the duct is oriented to open forward to easily receive the ram pressure.
In a vehicle including such a ram-air air-intake passage, during high-speed driving, air can be taken into the engine (combustion chamber) from outside efficiently by utilizing the ram pressure. However, since a portion of the duct which is located upstream of the air cleaner box in an air flow direction is long and a passage resistance of the air-intake passage is high, it is sometimes difficult to ensure a sufficient air-intake amount required for the engine during low-speed driving when the ram pressure is low. For example, when the vehicle is exiting a corner and is going to drive straight ahead, it is necessary to increase the amount of air supplied to the engine by opening a throttle valve to accelerate the vehicle. However, since the vehicle is exiting a corner at a low speed, the ram pressure is low and the passage resistance is significantly high, it is difficult to obtain a sufficient air-intake amount required for the engine quickly, even when the throttle valve is opened.